Dual band dipole radiator array

ABSTRACT

A dual band dipole radiator array includes a high band radiator array disposed on a dielectric layer for transmitting and receiving high band radar signals; a low band radiator array disposed on a front side of the high band radiator array for transmitting and receiving low band radar signals; a foam material between the low band radiator array and the high band radiator array for support; and a single aperture for both the low band radiator array and the high band radiator array for transmitting and receiving the radar signals, where the low band radiator array is comprised of a plurality of dipole structures disposed within the foam material and tuned to pass through high band radar signals to or from the high band radiator array.

FIELD OF THE INVENTION

The present invention relates generally to phased array antenna designand more specifically to dual band dipole radiator arrays.

BACKGROUND

An antenna array is a group of multiple connected antennas coupled to acommon source or load to act as a single antenna and produce a directiveradiation pattern. Usually, the spatial relationship of the individualantennas also contributes to the directivity of the antenna array. FIG.1 shows a diagram of one embodiment of a conventional antenna array 100.The antenna array 100 includes several linear arrays 104 housed in a(non-metallic) radome 102 that includes an aperture area for receivingand transmitting signals. Here, each linear array 104 is arrangedvertically with equal spacing between each other, which is determined bythe wavelength of the desired operating frequency of the antenna array100. Each linear array 104 is connected to its associated radiofrequency (RF) electronics circuitry contained in an external RFelectronics module 108, via an antenna feed 106. The RF electronicsmodule 108 is connected to external systems via a connection 110 forpower, control, and communications connections; and may be physicallymounted within the radome 102, or may be located remotely or outside ofthe antenna array 100.

An Electronically Scanned Array (ESA) is a type of phased array antenna,in which transceivers include a large number of solid-statetransmit/receive modules. In ESAs, an electromagnetic beam is emitted bybroadcasting radio frequency energy that interferes constructively atcertain angles in front of the antenna. An active electronically scannedarray (AESA) is a type of phased array antenna whose transmitter andreceiver (transceiver) functions are composed of numerous smallsolid-state transmit/receive modules (TRMs) or components. AESA antennasaim their beam by emitting separate radio waves from each module thatare phased shifted or time delayed so that waves interfereconstructively at certain angles in front of the antenna.

Typically, the basic building block of a conventional AESA is theTransmit/Receive module or TR module, which can be packaged to form anAESA antenna element, and may include a radiator to create a specificradiation pattern, receiver Low Noise Amplifier (LNA), transmit PowerAmplifier (PA), and digitally controlled phase or delay and gaincomponents. Several of these TR modules are placed on antenna panels ina grid format for transmitting and receiving radar signals. Digitalcontrol of the transmit/receive gain and phase allows an AESA antenna tosteer or point the resultant antenna beam without physically moving theantenna panel. Typical modern-day low cost AESA antenna panels employprinted circuit or patch radiators connected to surface mount MonolithicMicrowave Integrated Circuit (MMIC) devices that contain the LNA, PA andphase/gain control circuitry, which can be situated on a single printedcircuit board (PCB).

Typically, antenna arrays are designed in a platform or housing thatmust be sized for specific frequency and gain by tailoring thestructural elements of the platform for the specific frequency band. Forexample, larger antenna elements are needed for lower frequencies andsmaller antenna elements are required for higher frequencies, whileincreasing the number of antenna elements is necessary to increase theantenna gain. However, the antenna platform is generally a fixedstructure and typically cannot be modified to accommodate such changesor improvements in the design and therefore is not capable of easyadjustment of the frequency range and gain since they are generallyfixed in the structure. Additionally, since these antenna arrays arespecifically built for the specified frequency, gain, polarization, beamwidth, and other requirements, the lead time to make any design changesor performance improvements is very long.

FIG. 2 illustrates a typical architecture of a conventional radarantenna array. As shown, a plurality of power and beamforming buildingblocks 204/206 are arranged in an array 200 in rows and columns. Eachbuilding block 206 may include a number of transmit/receive integratedmultichannel module (TRIMM) cards and their associated power and signalselectronics cards including, for example 24 TRIMMs, a synthesizer card,a DREX (Digital Receiver Exciter) card, and an auxiliary powercontroller card. As a result, these designs require new unique radiatorand array structure and back structure for each radar frequency band andcannot be easily upgraded in performance and size at a later datewithout extensive rework. The power and beamforming network for eachblock (of 24 TRIMMs) would require extensive modification to theexisting power, signal and thermal management systems to add additionalmodular building blocks to a previously existing antenna system.

Some challenging radar applications require a radar that simultaneouslyoperates at two frequency bands, where the two frequency bands areseparated by at least an octave. Unfortunately, such a radar oftenrequires two independent apertures, and its cost and size are comparableto that of two radars. The two apertures also make transporting theradar difficult due to its size for tactical missions. Some conventionalmethods use a wideband element on a single aperture, that covers bothbands. However, this has the disadvantage of requiring a small latticeand a large number of modules at the low band, since the element latticeneeds to be sized for scan at the high frequency band. The wideoperating bandwidth also introduces Signal-to-Noise Ratio (SNR)limitations and intermodulation complexities.

SUMMARY

In some embodiments, the disclosed invention is a dual band dipoleradiator array for transmitting and receiving radar signals. The dualband dipole radiator array includes a high band radiator array disposedon a dielectric layer for transmitting and receiving high band radarsignals; a low band radiator array disposed on a front side of the highband radiator array for transmitting and receiving low band radarsignals; a foam material between the low band radiator array and thehigh band radiator array for support; and a single aperture for both thelow band radiator array and the high band radiator array fortransmitting and receiving the radar signals, wherein the low bandradiator array is comprised of a plurality of dipole structures disposedwithin the foam material and tuned to pass through high band radarsignals to or from the high band radiator array.

In some embodiments, each of the dipole structures includes one or moreresonating stubs tuned to an open circuit at high band frequencies. Theresonating stubs are transmission line or waveguide that are connectedat one end only and are tuned to an open circuit at high bandfrequencies. In some embodiments, each of the dipole structures includesone or more electronic chokes to pass through the high band radarsignals to the high band radiator array. The dipole structures mayinclude one or more inclined ribs that are at angle to a plane of highband radiator array and one or more perpendicular ribs that aresubstantially perpendicular to the plane of high band radiator array. Insome embodiments, the dipole structures may include one or more dipolestructures composed of solid metal and one or more dipole structurescomposed of hollow metal providing excitation to the low band radiatorarray.

In some embodiments, the high band radiator array and the low bandradiator array include patch radiators. The low band radiator array mayinclude: top radiator metal patches formed and spaced apart on adielectric substrate; bottom radiator metal patches formed and spacedapart on the dielectric substrate; and a metal ground plane includingopenings formed in the dielectric substrate. The spacing of the topradiator patches and the spacing of the bottom radiator patches arealigned with each other, and each opening covers entire spacings ofcorresponding top and bottom radiator patches.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings.

FIG. 1 shows a diagram of a conventional antenna array.

FIG. 2 illustrates a typical architecture of a conventional radarantenna array.

FIG. 3 depicts a subset of an exemplary dual band dipole radiator array,according to some embodiments of the disclosed invention.

FIG. 4 illustrates an exemplary low band dipole board mounted on a highband radiator array, according to some embodiments of the disclosedinvention.

FIG. 5 depicts an exemplary dual band patch radiator array with an FSS,according to some embodiments of the disclosed invention.

FIGS. 6A and 6B illustrate cross-sections of exemplary chokes, accordingto some embodiments of the disclosed invention.

FIG. 7 depicts an exemplary structure for high band patch radiators,according to some embodiments of the disclosed invention.

FIG. 8 illustrates an architecture of a modular and stackable antennaarray, according to some embodiments of the disclosed invention.

DETAILED DESCRIPTION

In some embodiments, the disclosed invention is a dual-band radiatorarray for radar applications, wherein a low band radiator array isplaced in front of a high band radiator array with both radiator arrayssharing a common radar aperture. In some embodiments, a low band patchradiator array having an outer frequency selective surface (FSS) istuned to a high band and being placed over or in front of a high bandpatch radiator array. The FSS on the surface of the low band patchradiator array passes the high band frequency to the underlying highband patch radiators. In some embodiments, the dual band radiator arrayachieves a low sidelobe performance in both bands with about 60-degreeconical scan volume. In some embodiments, a feed-through connectionbetween the low band radiators and the T/R modules via the high bandarray provides the signal feeds. This way, the radar can thenefficiently support dual band operation without having two apertures andwithout a very expensive wideband array that uses multi-octaveradiators. In some embodiments, the dual-band radiator array is modularat the sub-array level.

In some embodiments, a low band folded dipole structure/element isdisposed within a foam block over a high band patch radiator array,where the dipole structure includes stubs tuned to pass high bandfrequencies through to the underlying high band radiator array, forexample tuned to open circuit the dipole at the high band. Because ofthis the dipole radiators have low RF scattering cross sections at thehigh band frequencies to reduce the coupling between the dual bands. Thetwo apertures/phased arrays operate (in both transmit and receive modes)simultaneously by making the low frequency aperture transparent to thehigh frequency RF radiation.

In some embodiments, low band patch radiators are placed in front of thehigh band phased array. The low band patch radiators are madetransparent to the high band RF by placing a frequency selective surface(FSS) on their surfaces. The FSS geometrical features are integratedinto the low band coupled patch radiators, so that they are transparentto the high band, but behave as a metal plate at the low band.

In some embodiments, the low band radiators are dipole structures, whichare made transparent to the high band RF by incorporating tuned stubs orRF chokes, tuned for the high band. The tuned stubs or RF chokes breakup the dipoles into small segments at the high band frequencies, therebymaking the dipoles transparent to the high band RF signals.

FIG. 3 depicts an exemplary dual band dipole radiator array 300,according to some embodiments of the disclosed invention. As shown, ahigh band patch radiator array 304 is disposed on a dielectric layer 305to form the back of the dual band radiator array. A low band dipoleradiator array 302 is disposed on or in front of the high band radiatorarray 304 in a foam structure 306 that supports the low band radiatorarrays. These low band element feeds include a coaxial line embeddedinside one of the ribs/rods 307 of the dipole. At the end of the coaxialline, the center conductor is connected to a jumper strip 311, the otherend of which is connected to the other rib/rod 307 of that dipole. Thiseffectively excites the dipole at the low band frequencies, and is wellknown in the art. This coaxial line extents through the high bandradiator array, and is typically connected to the output of a low bandtransmit/receive module located behind the array. The coaxial low bandelement feeds protrude through the high band patch radiator arrangementat their edges. This way, both the low band dipole radiator array 302and the high band patch radiator array 304 share a singleaperture/radome 310. In some embodiments, the high band patch radiatorsin the array 304 are formed on the dielectric layer 305 by a patch metalfilm.

In some embodiments, the low band dipole radiator array 302 includessupports 307, for example rods or ribs, that are substantiallyperpendicular to the plane of high band patch radiator array 304 andinclude chokes or electric stubs 309. Rods/ribs 307 may be composed ofsolid metal, and as described above may contain a coaxial line thatconnects a low band transmit/receive module to the low band dipoleradiator. The low band dipole radiator array 302 also includes inclinedrods/ribs 303 that are at angle to the plane of high band patch radiatorarray 304 and also include chokes or electric stubs 309. The low weightfoam fills in the entire interior of the structure to provide a lowweight support structure, acting like air for both frequency bands.

The low band dipole radiator array 302 generates a radiation patternwith a radiating structure supporting a line current so energized thatthe current has only one node at each end. In some embodiments, thedipole radiator array 302 includes two identical conductive elementssuch as metal wires or rods. The driving current is applied to theserods by the radar transmitter, and the input signal to the radarreceiver is taken between the two halves of the dipole radiator, whereeach side of the feedline to the transmitter or receiver is connected toone of the conductors. In some embodiments, the low band dipole radiatoris excited by the coaxial line embedded inside one of the ribs/rods 307,as described above.

In some embodiments, the low band dipole radiator array 302 includes anarray of resonating stubs (309) located on the ribs or robs, forexample, transmission line or waveguide that are connected at one endonly and are tuned to an open circuit at low band frequencies. The inputimpedance of the stub may be modeled as capacitive or inductive,depending on the electrical length of the stub, and on whether it isopen or short circuit and therefore they function as capacitors,inductors and resonant circuits at desired radio frequencies.

In some embodiments, the low band dipole radiator array 302 is composedof a series of (electronic) chokes (309) that act as an open circuitthat blocks high band frequency currents, while passing low bandfrequency currents. By breaking up the high band frequency currents, thedipole is effectively broken up at the high band rf frequencies into acollection of small conductive RF scatterers, which greatly reduces itsRF scattering cross section relative to a conventional dipole. Thismakes this low band dipole array largely invisible to the high bandarray, and permits a single aperture to have both high and low bandfrequency operation.

FIG. 4 illustrates an exemplary low band dipole board mounted on a highband radiator array, according to some embodiments of the disclosedinvention. As shown, an array of high band (e.g., S-Band) patchradiators 404 are formed on a substrate 402. A plurality (only one isshown for simplicity) of low band (e.g., UHF) radiator printed circuitboards 406 are placed above the high band radiators as shown, one lowband radiator for each group of high band radiators 404. In the exampleof FIG. 4, a group of 8×8 or 64 high band radiators are shown. Each lowband radiator board 406 includes a dipole 412, a plurality of teeth 414and a support 410. Each radiator 404 includes a cut 408 to accommodatethe teeth 414 of a corresponding radiator board 406. A foam support, asshown in FIG. 3, may also be included for mechanical support.

FIG. 5 depicts an exemplary dual band patch radiator array with an FSS,according to some embodiments of the disclosed invention. As shown, alow band patch radiator array 502 is disposed on or in front of a highband radiator array 506 by support structures 508, such as support ribs.A frequency selective surface (FSS) 504, which is tuned to the high bandfrequency is disposed over or in front of the low band patch radiatorarray 502 and the high band radiator array 506. The FSS 504 on thesurface of the low band patch array 502 passes the high band frequencyto the underlying high band patch radiators, so that the low band patchradiators do not interfere with the high band transmit or receivesignals. However, the FSS behaves as a metal film at the low bandfrequencies so that the low band patch radiators operate as aconventional patch radiator array at the low band frequencies. Thesupport structures 508 can be directly driven by RF signals or cancontain an embedded coaxial cable to provide current to drive the lowband patch radiators. This way, both the low band patch radiator array502 and the high band patch radiator array 506 share a singleaperture/radome 512. In some embodiments, support structures 508, forexample ribs, may contain chokes tuned to the high band frequencies tomake the ribs transparent to the high band radiator array. A low weightfoam fills in the entire space between the low band patch radiator array502 and the high band patch radiator array 506 to provide a low weightsupport structure, acting like air for the frequency bands.

In some embodiments, any thin, repetitive surface designed to reflect,transmit or absorb electromagnetic fields based on the frequency of thefield may be used as the FSS 504. In some embodiments, the FSS is a typeof optical filter or metal-mesh optical filters in which the filteringis accomplished by the regular, periodic pattern on the surface of theFSS. The optical filter or the pattern on the surface of the FSS 504 isdesigned to be tuned to the (high band) frequency of the high bandradiator array 506.

Although, the low band radiators in FG. 5 and the high band radiators inFIG. 3 are described as patch radiators, one skilled in the art wouldrecognize that the radiators do not have to be patch radiators and otherknown methods of forming low band and high band radiators (other thanpatched radiators) are within the scope of the disclosed invention.

FIGS. 6A and 6B illustrate cross-sections of exemplary chokes, accordingto some embodiments of the disclosed invention. As shown, a plurality ofchokes 602 are formed around a metal support 606 with a diameter of C,where the distance between each choke is shown as B. As shown in FIG.6A, one end 607 of each choke 602 is connected to a metal support 606,for example, a rod/rib, while the other end 608 is left open. The openends 608 include a dielectric layer 604 with a thickness of d and lengthof A that is shorter than the length of the chokes but fills the gapbetween the choke 602 and the metal support 606. In some embodiments,alternate chokes are mirror images of each other, namely the end 608 mayface the end 608 of the adjacent choke, and the end 607 may face the end607 of the other adjacent choke.

The chokes 602 have no or negligible effect for the low frequency band;however, they behave as open circuits for the high frequency band topass high band frequencies through to the underlying high band radiatorarray.

In some embodiments as depicted in FIG. 6B, the chokes 620 are formedaround a metal support 606, but are connected to the metal support 606in their center, and include dielectric layer or inserts 627 and 628 atboth ends of each choke 606.

Assuming that λ is the wavelength of the high frequency band, the designparameters for the chokes are as follow:

-   -   d<<λ/4    -   A≈λ/(4*ε^(1/2))    -   D<<λ/4    -   B<λ/4,    -   C<<λ/4 consistent with power handling

The design parameters D and C are selected as small (thin) as possibleconsistent with power handling of the radar system. However, B isselected as not being so small that the capacitance of the joint betweenadjacent chokes increases the RF conductance at the high band. In someembodiments, the chokes are cylindrical.

FIG. 7 depicts an exemplary top view 700 and an exemplary cross sectionview 701 of a frequency selective surface (FSS), according to someembodiments of the disclosed invention. As shown, upper and lowerradiator (metal) patches 706 are formed and spaced apart on a dielectricsubstrate 702. The spacing of the upper radiator patches 706 and thespacing of lower radiator patches 706 on the dielectric substrate 702correspond to (aligned with) each other, as depicted. Dielectricsubstrate 702 includes a metal ground plane 704. The metal ground plane704 includes openings (apertures) 708, each covering the entire spacingof corresponding upper and lower radiator patches 706. The radiatorpatches 706 are excited by electromagnetic waves and start radiating,when the high frequency band is turned on. Note that the metal patchesand the openings in the ground plane can be any shape, for example,round as shown in FIG. 7, square or the like.

FIG. 8 illustrates an architecture of a modular and stackable antennaarray 800, according to some embodiments of the disclosed invention. Asshown, the antenna array 800 includes four modular and stackable antennaarray blocks 806. Each modular and stackable antenna array block 806includes a plurality of antenna elements/radiators (for example, 802),as shown by the modular block 806). Each modular and stackable antennaarray building block 806 may include a number of transmit/receiveintegrated multichannel module (TRIMM) cards and their associated powerand signals electronics cards that is a fully functional stand-aloneradar antenna array, with its own self-supporting structure.

In some embodiments, the modular antenna structure and supportingelectronics 802 reside within the volume behind the active antennaregion 806, allowing one antenna array block to be stacked on top of, ornext to, another antenna array block to create a single, largermonolithic antenna with no disruption of antenna array's latticespacing. Power, cooling and beamforming 804 are connected in parallel toeach modular antenna array block and therefore, eliminating thedependency of one antenna array block on the adjacent antenna arrayblock.

The modular and stackable antenna blocks may be combined (e.g. stackedon, or placed next to) together to produce any desired size antennaarray 800 and thus minimizing the initial investment costs whilemaintaining the ability to easily increase the size and sensitivity andthus capability of the antenna array, as required by differentapplications. Each modular and stackable antenna block operates the sameregardless of the assembled array size. This way, additional antennablocks can be added later without impact to the existing system'sstructure, support electronics or thermal management.

It will be recognized by those skilled in the art that variousmodifications may be made to the illustrated and other embodiments ofthe invention described above, without departing from the broadinventive step thereof. It will be understood therefore that theinvention is not limited to the particular embodiments or arrangementsdisclosed, but is rather intended to cover any changes, adaptations ormodifications which are within the scope of the invention as defined bythe appended drawings and claims.

What is claimed is:
 1. A dual band dipole radiator array fortransmitting and receiving radar signals comprising: a high bandradiator array disposed on a dielectric layer for transmitting andreceiving high band radar signals; a low band radiator array disposed ona front side of the high band radiator array for transmitting andreceiving low band radar signals; a foam material between the low bandradiator array and the high band radiator array for support; and asingle aperture for both the low band radiator array and the high bandradiator array for transmitting and receiving the radar signals, whereinthe low band radiator array is comprised of a plurality of dipolestructures disposed within the foam material and tuned to pass throughhigh band radar signals to or from the high band radiator array.
 2. Thedual band dipole radiator array of claim 1, wherein each of theplurality of dipole structures includes one or more resonating stubstuned to an open circuit at high band frequencies.
 3. The dual banddipole radiator array of claim 2, wherein the one or more resonatingstubs are transmission line or waveguide that are connected at one endonly and are tuned to an open circuit at high band frequencies.
 4. Thedual band dipole radiator array of claim 1, wherein each of theplurality of dipole structures includes one or more electronic chokes topass through the high band radar signals to the high band radiatorarray.
 5. The dual band dipole radiator array of claim 1, wherein theplurality of dipole structures includes one or more inclined ribs thatare at angle to a plane of high band radiator array and one or moreperpendicular ribs that are substantially perpendicular to the plane ofhigh band radiator array.
 6. The dual band dipole radiator array ofclaim 1, wherein the plurality of dipole structures includes one or moredipole structures composed of solid metal and one or more dipolestructures composed of hollow metal providing excitation to the low bandradiator array, using a coaxial line that is embedded inside the hollowmetal dipole structure.
 7. The dual band dipole radiator array of claim1, wherein each of the plurality of dipole structures includes a lowband radiator printed circuit board disposed on each group of high bandarray radiators.
 8. The dual band dipole radiator array of claim 1,wherein the high band radiator array is an array of high band patchradiators.
 9. The dual band dipole radiator array of claim 1, whereinthe low band radiator array is an array of low band patch radiators. 10.The dual band dipole radiator array of claim 1, wherein each of the lowband radiators comprises: a coaxial Transverse Electromagnetic (TEM) lowband element feed that protrudes through the high band radiator array atone edge, wherein the TEM low band element feed includes a coaxial lineembedded inside a rib of the dipole structure of the low band radiator.11. The dual band dipole radiator array of claim 10, wherein at a firstend of the coaxial line, a center conductor is connected to a jumperstrip, and a second end of the coaxial line is connected to a second ribof the dipole structure of the low band radiator.
 12. The dual banddipole radiator array of claim 10, wherein the coaxial line extentsthrough the high band radiator array and is connected to an output of alow band transmit/receive module located behind the high band radiatorarray.
 13. The dual band dipole radiator array of claim 10, wherein thelow band dipole radiator is excited by the coaxial line embedded insideone of the ribs.